1. Field of the Invention
The present invention relates to an image-forming apparatus and an image-forming method, in which an electrophotographic system is adopted. More specifically, the present invention relates to an image-forming apparatus used for forming color and monochrome images, such as a copying machine, a printer and a facsimile, and a corresponding image-forming method. In particular, the present invention relates to an image-forming apparatus and an image-forming method, which form an image by transferring a toner image formed on an image-supporting member onto a recording medium.
2. Description of the Related Art
In the conventional image-forming apparatus that uses an electrophotographic system, an image-forming apparatus, in which an intermediate transfer system is adopted has been known. In this system, upon transferring a toner image on a photosensitive member onto a recording material, an intermediate transfer member is used. More specifically, after a toner image on the photosensitive member has been once primary-transferred onto the intermediate transfer member, the toner image on the intermediate transfer member is secondary-transferred onto a recording material. In most cases, the intermediate transfer system is adopted as a multiple transfer system for toner images of respective colors in a so-called full-color image-forming apparatus in which a document image, which has been color-decomposed, is reproduced by a subtractive color mixing process using toners having respective colors of black, cyan, magenta, yellow and the like. However, in the multiple transfer system by the use of the intermediate transfer member, two transferring processes, that is, a primary transferring process and a secondary transferring process, are required, and since toner images of four colors are superposed on the intermediate transfer member, a problem arises in which a defective image tends to be formed due to defective transfer.
In order to solve this problem, a technique (JP-A No. 2007-17666) in which an inorganic compound layer is formed on the surface of an intermediate transfer member by using a plasma CVD method and a technique in which a ceramic film is formed on the surface of an intermediate transfer member have been proposed. By using such techniques, the peeling property of a toner image from the intermediate transfer member is improved so that the transferring efficiency onto a recording material or the like can be improved.
In the image-forming apparatus that uses the electronic photographic system, image-stabilizing control is generally carried out in order to maintain the image density within a predetermined range. More specifically, a predetermined toner pattern is formed on an image-supporting member typically represented by an intermediate transfer belt or the like, and this is detected by an optical sensor. The optical sensor includes a light-source unit that applies light having a specific waveform length to the peripheral face of the image-supporting member and a light-receiving unit that receives its reflected light. Light is applied onto the toner pattern on the peripheral face of the image-supporting member from the light-source unit of the optical sensor, and the light-receiving unit receives its reflected light so that based upon the quantity of received light, the amount of adhered toner (toner density) of the toner pattern is detected. Based upon the results, process conditions are altered so that the image density can be maintained within the predetermined range.
However, in the case when a thin-film layer, such as an inorganic compound layer and a ceramic film, is formed on the surface of the intermediate transfer member as described above, when the image-stabilizing control is carried out, an optical interference occurs due to influences of optical characteristics between the optical sensor and the thin-film layer. Moreover, since, upon detecting the toner pattern, the detecting operation is carried out, with the intermediate transfer member being driven, the optical thickness of a pattern detection area fluctuates due to fluctuation factors, such as thickness nonuniformity and jouncing of the intermediate transfer member thin-film layer, with the result that the optical interference becomes conspicuous. In particular, since fluctuations in reflectance due to the thickness nonuniformity of the thin-film layer occur remarkably, the calibration of the optical sensor and the detection of the toner pattern are not carried out accurately, resulting in a problem of failure in maintaining the image density within the predetermined range.